[sdiy] More new Alfa chips - CEM3394

Tim Ressel timr at circuitabbey.com
Thu Apr 4 17:46:57 CEST 2019

you can get an 8-channel 8-bit DAC with SPI for about $2. no need to 
muck about with muxes.


On 4/4/2019 5:14 AM, Neil Johnson wrote:
> Hi Rich,
>> When I saw "Microprocessor controllable..." in the datasheets for these
>> CEM chips I was initially expecting to see an SPI interface! :-(
> Indeed not, as they say (AS3394E):
>> Thus interface to a microprocessor system may be accomplished simply with a single DAC, 4051-type CMOS multiplexer, and 8 hold capacitors.
> That said, for a polyphonic synth it is actually quite useful to have
> voltage control of these parameters, in EGs for example, where each
> parameter is common across all voices so you hang the controls off a
> voltage bus.  For example this is how the Siel Opera6 does things,
> with all the SSM EGs driven off common voltages for the A, D, S and R.
> If you did this with SPI then you would either need some sort of
> addressing scheme (in that case use I2C), OR you end up with a huge
> mass of slave select lines!!  And you've now increased the cost of the
> silicon by putting logic (another voltage rail) and some number of
> DACs plus reference on the die.
> Cheers,
> Neil

--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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